The field of the invention is the field of Radio Frequency (RF) or Microwave communication of data and control information between a Base Station and a plurality of remotely located RF Transponders (Tags).
Identification and Location Transponders (Tags) such as radio frequency (RF) Tags have been used in a multiplicity of ways for locating and identifying accompanying objects and transmitting information about the state of the object. It has been known since the early 60's that electronic components could be powered by RF power received by an antenna and rectified by an RF diode. In the 70's, suggestions to use tags with read/write memories which back scattered the incoming RF were made. In the 70's suggestions were also made to convert part of the incoming RF radiation to a harmonic of the incoming signal, and rebroadcast this new frequency to communicate the tag information. Presently available technology uses a number of different systems, each having tags and base stations which use different kinds of tags using different frequencies, different read and write codes, tags with electronics powered with batteries, tags which transmit a different carrier frequency than does the base station, tags which communicate by changing magnetic field, by sound and ultrasound fields, etc.
Prior art systems send power from the base station to energize the tags, and the tags modulate the loading on the tag antennas to communicate the information contained in the tag memory, or the information measured by the tag, back to the base station.
Prior art systems can interrogate the tags if more than one tag is in the field. U.S. Pat. No. 5,214,410, hereby incorporated by reference, teaches a method for a base station to communicate with a plurality of Tags.
The prior art teaches a method to interrogate a plurality of tags in the field of the base station. The tags are energized, and send a response signal at random times. If the base station can read a tag unimpeded by signals from other tags, the base station interrupts the interrogation signal, and the tag which is sending and has been identified, shuts down. The process continues until all tags in the field have been identified. If the number of possible tags in the field is large, this process can take a very long time. The average time between the random responses of the tags must be set very long so that there is a reasonable probability that a tag can communicate in a time window free of interference from the other tags.
The continuing march of semiconductor technology to smaller, faster, and less power hungry circuits has allowed enormous increases of function and enormous drop of cost of such tags. Presently available research and development technology will also allow new function and different products in communications technology. There is no technology in place to handle the many different products which could be allowed by the technology.
Presently, each system of tags has matching base stations, and thus the tags of one system can not communicate information to a base station of another system. Within any given system, the tags have the same physical and software characteristics, i.e. the number of bits of read/write memory is the same, and the information stored on the tag is stored the same unstructured way for every tag in the system.